Classes and Objects. Instructor: 小黑

Transcription

1 Classes and Objects Instructor: 小黑

2 Files and Streams in C : 1 #include <stdio.h> int main( void ) { 5 char input[ 5 ]; 6 7 FILE *cfptr; 8 9 if (( cfptr = fopen( a.txt", r )) == NULL ) { 10 printf( "File could not be opened\n" ); 11 } 12 while (!feof( stdin ) ) { 13 fscanf( cfptr, "%s, input); 14 } return 0; 17 } in C++, we can do like this: 1 #include <fstream> 2 using namespace std; 3 4 int main( void ) { 5 char input[ 5 ]; 6 7 fstream fin ( "a.txt, fstream::in); 8 9 if ( fin.is_open() == false ) { 10 printf( "File could not be opened\n" ); 11 } 12 while ( fin.good() ) { 13 fin >> input; 14 } return 0; 17 }

3 Files and Streams in C : 1 #include <stdio.h> int main( void ) { 5 char input[5] = {"test"}; 6 7 FILE *cfptr; 8 9 if (( cfptr = fopen( "a.txt", "w" )) == NULL ) { 10 printf( "File could not be opened\n" ); 11 } fprintf( cfptr, "%s\n", input); return 0; 17 } in C++, we can do like this: 1 #include <fstream> 2 using namespace std; 3 4 int main( void ) { 5 char input[5] = {"test"}; 6 7 fstream fout ( "a.txt", fstream::out); 8 9 if ( fout.is_open() == false ) { 10 printf( "File could not be opened\n" ); 11 } fout << input << endl; return 0; 17 }

4 Files and Streams More IOstream library function you can use: get getline read unget read/write seekg/seekp flush

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6 Structures V.S. Classes The class is a foundation of OOP. It is very similar to the expanded structures that group related data and functions together. Struct Employee { char name[10]; int salary; float height; }; class Employee { char name[10]; int salary; float height; };

7 Classes and Objects C++ provides three ways of accessing class members: Public: can be accessed by members of its class as well as members of any other class and non-member functions, including main() Private: can only be accessed by other members of the same class. Protected: when dealing with inheritance class Employee { public: Employee() {} Employee(char *name) {} ~Employee() {} char * getname() {}... private: char _name[10]; int _salary; float _height; };

8 Classes and Objects When an object of the class is declared, the constructor is automatically called. Employee em1; Employee em2( John ); class Employee { public: Employee() {} Employee(char *name) {} ~Employee() {} char * getname() {}... private: char _name[10]; int _salary; float _height; };

9 Define methods Following is a sample class: class XYZCoord { public: XYZCoord( int x, int y, int z) { } _x = x, _y=y, _z=z; int getx() { return _x; } void output() { } private: int _x, _y, _z; }; cout << ( << _x <<, << _y <<, << _z << ) << endl; Define with a header file: class XYZCoord { public: XYZCoord( int x, int y, int z); int getx(); void output(); private: int _x, _y, _z; }; XYZCoord::XYZCoord(int x, int y, int z) { _x = x, _y=y, _z=z; } int XYZCoord::getX() { return _x; } void XYZCoord::output() { cout << ( << _x <<, << _y <<, << _z << ) << endl; }

10 Purpose of Constructors The constructor is a simple and automatic way to initialize the objects. int main() { Employee myemployee; myemployee.init(); class Employee { public: void init() {...}... private: char _name[10]; int _salary; float _height; }; } return 0;

11 Use of Constructors We can define a default constructor separately or by providing default arguments for all parameters. class Employee { public: Employee(); Employee(char *name = Blackie, int salary = 100, private: }; char _name[10]; int _salary; float _height; float height = 170.5);

12 Destructors There can be only have one Destructor. Destructor has no parameter and no return type. It s usually used to release resource. class Player { public: Player( ) { char *name = new char[strlen(name)+1]; strcpy ( _name, name); } ~Player() { delete [] _name; } private: char *_name; }

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14 Today s practice Define a class Pet Data member: _name, _level; Default values of _name and _level are Lucky and 1, respectively. User can pass name and level when constructing a Pet object. Define a class Player Data member: _name, _level, _pet; Default values of _name and _level are player and 1, respectively. User can pass player s name, player s level, pet s name and pet s level when constructing a Player object.

15 Today s practice ( contd.) Create an input.txt file that as follow: Ann 50 Molly 46 Tom 8 Max 7 Sam 20 Rocky 13 Ted 5 pepe 1 Each line contains four attributes: player s name, player s level, pet s name, pet s level. Create an output.txt file that save your data before exit.

16 Today s practice ( contd.) Provide a simple UI as follow: 1. Add new player Input player s name. ( No need to input level, pet s name and pet s level ) 2. Show all players Print all player s name, level and their pet. 3. Save & Leave Save all information in output.txt file like input.txt s format.

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